1. Field of the Invention
The present invention generally relates to controlled processing of materials and, more particularly, is concerned with a method of controlling hydrocarbon release rate by maintaining target oxygen concentration in discharge gases so as to thereby convert successive batches of materials of widely varying energy content into substantially harmless gases and carbon-free residue ash.
2. Description of the Prior Art
The problem of disposal of waste matter involves a material processing challenge that is becoming increasingly acute. The primary material processing methods of waste disposal have been burning in incinerators and burial in landfills. These two material processing methods have severe disadvantages. Burning of waste liberates particulate matter and fumes which contribute to pollution of the air. Burial of wastes contributes to the contamination of ground water. A third material processing method is recycling of waste. Although increasing amounts of waste are being recycled, which alleviates the problems of the two primary material processing methods, presently available recycling methods do not provide a complete solution to the waste disposal problem.
The problem of disposal of biomedical waste materials is even more acute. The term "biomedical waste materials" is used herein in a generic sense to encompass all waste generated by medical hospitals, laboratories and clinics which may contain hazardous, toxic or infectious matter whose disposal is governed by more stringent regulations than those covering other waste. It was reported in The Wall Street Journal in 1989 that about 13,000 tons a day of biomedical waste, as much as 20% of it infectious, is generated by around 6,800 U.S. hospitals.
Hospitals and other generators of biomedical waste materials have employed three main material processing methods of waste handling and disposal: (1) on-site incineration with only the residue transferred to landfills; (2) on-site steam autoclaving and followed by later transfer of the waste to landfills; and (3) transfer of the waste by licensed hazardous waste haulers to off-site incinerators and landfills. Of these three main material processing methods, theoretically at least, on-site disposal is the preferred one.
However, many hospital incinerators, being predominantly located in urban areas, emit pollutants at a relatively high rate which adversely affect large populations of people. In the emissions of hospital incinerators, the Environmental Protection Agency (EPA) has identified harmful substances, including metals such as arsenic, cadmium and lead; dioxins and furans; organic compounds like ethylene, acid gases and carbon monoxide; and soot, viruses, and pathogens. Emissions of these incinerators may pose a public health threat as large as that from landfills.
Conventional incinerators most commonly are designed to operate above a certain temperature, such as 1200.degree.-1400.degree. F., to comply with requirements of the permit laws of many states. The reason for this requirement is that conventional thinking has been that operation of incinerators at such elevated temperatures will substantially eliminate the release of most harmful substances. This may have been true where the materials being consumed by the incinerator were assumed to be fairly uniform in terms of energy content and thus burned more or less evenly. However, this is the exception and not the normal situation today, particularly in the case of biomedical waste materials which can range from wet paper towels and steel surgery tools to plastic syringes and containers of saline solution. The thermal processing of these materials by temperature control alone will ordinarily result in the inability to control the hydrocarbon release rate and the repeated emission of un-burned hydrocarbons, typically visible as periodic puffs of black smoke, which is unacceptable under most current environmental regulations.